In EUV lithography devices, reflective optical elements for the extreme ultraviolet (EUV) wavelength range (e.g. wavelengths between approximately 5 nm and 20 nm), such as photo masks or mirrors on the basis of multi-layer systems, are used for the lithography of semiconductor components. Since EUV lithography devices generally comprise a plurality of reflective optical elements, it is desirable that the latter have a reflectivity which is high to ensure a sufficiently high overall reflectivity.
Plasma sources, among others, can serve as radiation sources. The plasma can be generated by discharge (DPP source) or, preferably, by laser excitation (LPP source). To this end, material droplets are exposed to intensive laser radiation in order to excite them to form a plasma which, among other things, emits radiation in the EUV wavelength range. In order to enhance the portion of EUV radiation available for EUV lithography, use is made, among other things, of mirrors for grazing incidence. These generally are substrates with a reflecting coating made of metal. By way of example, such mirrors are described in EP 1 882 984 A1. There, for example, reflecting coatings made of molybdenum, ruthenium, rhodium, palladium, niobium or zirconium are described, which achieve reflectivities of more than 60% for angles of incidence of up to 15°, in part up to 20°, in relation to the mirror surface.